12v dc PWM Speed Control

[ericlouie1]

I was looking at another post for my exact same application, but the schematics were a little vague, just wanted some opinions on my take on it.
I am building a 12vdc PWM speed controller, single direction. The input voltage on the system will be around 13.3 volts. The estimated current draw of the motor is between 25 and 35 amps, giving me a worst cast power depand of around 500 watts. A bypass will be included on the circuit to allow for full speed of the motor at the push of a button, to clear chunks and jams. Either fuse or breaker protection is needed as well, 10amps for the PWM, and 40 for the motor.

Took me a little bit to understand the concept of a mosfet and the PWM system but i think I have a pretty good grasp on it now.

I'm not exactly sure if all my component selections are correct.
I am shooting for a frequency of 10K, seems to be the magic number for noise and whatnot.
I get this using values of .096uf for the caps and 1.5K POT.
Do i use this value for the rest of the capacitors in the circuit, or will .01 uf caps be sufficient for this task?
Not exactly sure what the purpose of the 10k resistor for r2.....
For the mosfets i was thinking about two of three of these, hooked up the a heat sink and possible fan- STP200nf04
(wont let me post link)
40v source breakdown, 120 amps, 310 watts
For the timer, either a LM555 or a TLC555, the latter has a slightly higher power dissipation and temperature rating.
Gotta post more to do pic or links, drats.

---------- Post added at 05:04 ---------- Previous post was at 04:45 ----------

Probally going to stuff this into some kind of project box, just gotta figure out what size i will need with the heatsinks and fan and whatnot.

 

[ljcox]

Attached is the circuit of a 12 ~ 24 Volt, high current (up to 40 A) PIC controlled motor controller that employs PWM.

It was featured in the March 2008 edition of Silicon Chip.

A copy of the article, software, PCB layout, etc. can be obtained from Silicon Chip Electronics Magazine for Hobby Electronics, Computing, Kits and Projects.

 

[ericlouie1]

Thank you, that on is a bit more complicated than what i had thought I might need, I still have to wait a post until i can post my scheme.

---------- Post added at 07:38 ---------- Previous post was at 07:36 ----------

WOW, took a closer look at it and looked at the feedback circuitry and display module. I might be able to simplify it a bit to make it work for me. I took the thought of multiple mosfets from previous posts and applied it to my design as well.....Well, not exactly a design, just a pretty drawing with not much in the way of specs.



BOOYAH
The third mosfet is the potentially optional one, I was reading about how too many can cause a problem with the way the circuit turns on and off, still not exactly sure how to figure that particular point out though.
Also, 87 on the relay goes directly to ground for the bypass. Thats at least one missed little detail that that I found.
Also, I saw a post on the other thread like this where someone recommended a resistor between terminal one and ground, whats the purpose of this, and what would be a good valuve to use.

I am not a total dum-dum with electronics, its just been a while since my electrical components teacher was jambing my brain with info, and i've had not practice with the component level, only the "replace the board/module/widget, it seems bad" end out it.

I sincerely appreciate any and all helpful info though!

 

[ljcox]

I suggest that you consider using an IGBT rather than a MOSFET.

They are a combination of a Bipolar transistor & a MOSFET & thus combine the advantages of both.

I have attached an example.

 

[ericlouie1]

So would three of these be enough to work?
HGTP20N60A4 Fairchild Semiconductor Transistors IGBT

 

[ljcox]

So would three of these be enough to work?
HGTP20N60A4 Fairchild Semiconductor Transistors IGBT

You should only need one.

You need to do the thermal calculations.

Look at the data sheet and calculate what the maximum safe current is.

The data sheet gives you the thermal resistance between the junction & case, you need to select a heat sink that has a thermal resistance to the ambient that is low enough to keep the chip temperature below the recommended safe limit.

 

[ThatBozGuy]

You only need One

 

[ericlouie1]

Aye yi yi.
Its taking a bit for my brain to get a grasp on the "concept" of how these function, and how to properly select the component so that I don't let the smoke out.
Since I'm operating on a 12v system, won't that change the amperage rating if I go with a model with a 600V max collector-emitter voltage
I'm looking at a lot of these and they have 100 to 250 watts worth of dissipation, but i guestimate my system to be in the neighborhood of 500watts.
I need a bit of reading to figure out all of this, as selecting the right type of chip for this job is currently over my head.
Thanks for all the info so far, but I need a lil bit more...not giving up, but i just want to understand it a little better.